HVCA DW/143 Apreactical guide to -
DUCTWORK LEAKAGE TESTING Based on the requirements of DW/142 specification for sheetmetal ductwork.
1983
COPYRIGHT ⓒ 1983 by the Heating and Ventilating Contractors' Association All rights reserved
HEATING AND VENTILATING CONTRACTORS' ASSOCIATION Esca House, 34 Palace Court,
London W2 4JG
Obtain Obtainabl able e from from : HVCA HVCA Pu Publi blicat cation ions, s, OLD Mansion House, Eamont Bridge, Penrith, Cumbria, CA10 2BX Telephone : Penrith (0768)64771 (0768)64771 Telex : 64326 64326
page 1 of 40
Contents
Part One
Page
Acknowledgements
4
Preface
5
Financial Caution
6
Practical Guide to leakage testing
7~ 8
Example of complete test sheet
9
Hints on leakage testing
1 0~ 11
Part Two Air leakage from-ductwork
13 ~ 15
Nomogram converting area basis to percentage of airflow Air leakage testing procedure
16 17 ~ 18
ACKNOWLEDGEMENTS The HVCA records its appreciation and thanks to the persons and organisations who have freely contributed to this work, and in particular to the members of the Drafting Panel. DW/143 Drafting Panel J.H.G Gardner (Chairman) K, Angood P. Doyle K, Wheatley K, Waldron H. Brockiehurst H. Brierley J.M Paynton (Former Secretary, Duct Work Group) R,J,Miller (Secretary, Duct Work Group)
page 2 of 40
Contents
Part One
Page
Acknowledgements
4
Preface
5
Financial Caution
6
Practical Guide to leakage testing
7~ 8
Example of complete test sheet
9
Hints on leakage testing
1 0~ 11
Part Two Air leakage from-ductwork
13 ~ 15
Nomogram converting area basis to percentage of airflow Air leakage testing procedure
16 17 ~ 18
ACKNOWLEDGEMENTS The HVCA records its appreciation and thanks to the persons and organisations who have freely contributed to this work, and in particular to the members of the Drafting Panel. DW/143 Drafting Panel J.H.G Gardner (Chairman) K, Angood P. Doyle K, Wheatley K, Waldron H. Brockiehurst H. Brierley J.M Paynton (Former Secretary, Duct Work Group) R,J,Miller (Secretary, Duct Work Group)
page 2 of 40
PREFACE Ductwork Specification DW/142, published by the HVCA in 1982, provides for the first time in a long series of such publications for leakage limits over the whole range of air pressures covered by the specification and (where required) a test procedure to establish e stablish conformity. Although leakage testing of high-pressure ductwork is mandatory in DW/142 (as was the case in previous ductwork specifications issued by HVCA) the leakage testing of ductwork designed to operate at low and medium pressure is required only where so specified in individual job specifications. With the introduction of four pressure classifications in DW/142 it is hoped that the designer,having selectional control of constructional srandards,will find leakage testing an unnecessary contract expense with fegard to low and medium pressure ductwork. However,it is possible that initially the advent of more stringent constructional requirements may be followed by an increased demand by clients and specifiers for the testing of low-and medium-pressure ductwork and this booklet has been prepared in order to assist ductwork contractors to minimise the cost of this unfamiliar operation. It will be noted that the leakage limits speccified in Appendix A of DW/142 are expressed in litres per second per square metre of duct area. It is however possible that some ductwork specifications will still quote leakage limits as a percentage of air flow. In order that the area basis can be converted to a percentage equivalent a nomogram from DW/142 has been reproduced in this booklet on Page 16. Ductwork contractors faced with a job calling for leakage testing should take this requirement very seriously and satisfy themseleves as the job progresses that the required leakage rate or rates are within the limits set by the designer or the client. The cost of making good an installation that has been found on completion to have failed in this respect can be very exprensive indeed. DW/142 specifies leakage limits for the ductwork alone, not for the complete air distribution system. This is because the ductwork contractor has no control over the leakage characteristics of the various components which go to make up the whole of the air distribution system. Where a job specification calls for a leakage limits for the whole system. It will be for the designer or client to ensure that the leakage rates of the components are also within the required limits.
J.H.G. Gardner, Chairman, Executive Committe Duct Work Grop, 1982/83
Part One - A Pract ca gu
e to page 3 of 40
ductwork leakage testing 1. GENERAL With regard to air leakage, the responsibility for ensuring the achievement of a satisfactory job is divided between the Drawing Office, the Factory and the Site Erection Operatives. It is essential that there is full co-operation between them.
2. THE DRAWING OFFICE THE DRAWING OFFICE must : 2.1
Establish Establish with the client client or his his represent representative atives s the the class class of ductwo ductwork rk called called for in the job specification, i.e.: Class A : up to 500 Pa positive positive Class B : up to 1000 Pa positive Class C : up to 2000 Pa positive Class D : up to 2500 Pa positive
2.2
Establ Establish ish with with the client client or or his repres representa entativ tive e that the the required required leaka leakage ge rate or rates are for the ductwork alone .i.e. excluding dampers,fire dampers, air handling units, fans, heater batteries, silencers, terminal boxes, etc. Additionally, establish the type of gasket material required in relation to the pressure class/velocity of the system. Note : - Specific gasket material may be required in locations such as clean rooms, hospitals etc. If a leakage limits is laid down for the whole system, it will be for the client or the designer to ensure that leakage characteristics of the components are acceptable.
2.3
Agree Agree with with the client client of of designe designerr the test test press pressure ure for for eath sect section ion of the the installation. (Note (Note that whilst duct construction) construction) Specification is related to the highest test class of the duct installation it is important that each duct test zone should only be tested to a pressure to cover the mean working pressure of that particular section of ducting - see A.2.5(b)
2.4
Decide Decide on the the best way way to isol isolate ate the the instal installat lation ion into into test test zones zones.. When doing so, the drawing office should bear in mind the test pressure called for, the allowable air losses, the work sequence on site and the capacity of the test equipment.
2.5
Arrang Arrange e for the the supply supply of of suitab suitable le blankin blanking g medium, medium, e.g. e.g. heav heavy-d y-duty uty polythene sheet. page 4 of 40
2.6
Make sure that all test points and blanking devices can be reached with the minimum of difficulty after the ductwork has been installed.
2.7
To ensure that a reading can be obtained, plan test sections to have a permitted loss of approximately 25 per cent less than the total volume generated by the test rig at the pressure required for each section.
2.8
Provide the erectors with details of the test zones, duct operating pressure and test pressure; and indicate the nature of the blanking devices, gasket material and seaiant to be used.
2.9
Prepare test sheets giving the information called for on the sample test sheet shown on page 9. This information should indicate the test content, the surface area of the ductwork to be tested, and permitted loss for each section to be tested (this loss is to be expressed in litres per second per square metre of the ductwork).
3. THE FACTORY 3.1
Ductwork specification DW/142 requires the sealing of more joints than was the case in previous specifications. Care must therefore be taken to make components with a good fit. and to use only enough sealant to make a satisfactory joint. A poor fit cannot be remedied by the use of more sealant - it will not work.
3.2
Seal all longitudinal seams, laps, cross joint, rivets and duct penetations generally, in accordance with the requirements of DW/142.
3.3
Make sure that sealant is properly applied to the ends of all lock forms nd other types of longitudinal seam, and to the corners and junctions between those seams and the cross joints.
3.4
Take special care to have as small a clearance as possible where are penetrations of the duct, as for example, damper spindles.
3.5
First and seal branch connections carefully, as required by DW/142.
3.6
To be sure of minimum leakage, special care must be taken in the fitting and sealing of access doors and panels etc.
3.7
To avoid the danger of breaking the seals, the ductwork when ready for despatch to site must be handled and loaded carefully.
page 5 of 40
4. SITE WORK For full details of procedure see Appendix B Pages 17 and 18 and the diagram on Page 10 and 11.
4.1
Understand the proper use of the testing. It is expensive precision equipment. The instructions must be read carefully and the equipment handled in responsible manner.
4.2
Make sure that the right type of test rig is available for the job. A rig suitable for high pressure leakage testing is seldom suitable or economic for testing low-or medium-pressure ductwork, and vice versa.
4.3
Note that leakage testing is always done under positive pressure even when the ductwork is to operate under negative pressure.
4.4
Before erection Inspect all duct sections to make sure that factory applied sealants have not been damaged in transit. Makr good where any damage is noticed.
4.5
Ensure the correct gasket material has been supplied for your situation and the application is in accordance with the manufacturer's instructions. Check with the drawings and specifications as to where sealants are to be used on the cross joints, and then apply the sealants as necessary. (Use only as much sealant as will do the job - too much sealant is as bad as too little.)
4.6
Pay special attention to the sealing of joints that will be difficult to reach after erection of the ductwork.
4.7
Fix the blanking plates or other types of temporary seal in the positions shown by the Drawing Office. (Again, make sure that the blanking material can be reached when it has to be removed.)
4.8
At the earliest opportunity agree with the client or his clerk of works on a progressive testing programme.
4.9
To ensure that the ductwork has been correctly manufactured and site sealant correctly applied it is essential that a preliminary test is carried out on each section of the work at the earliest opportunity - before presentation to the elient.
4.10 If these preliminary tests show that the leakage is over the limit, then ;
page 6 of 40
4.10.1
a) b) c) d)
Look for any obvious places where there may be leaks, for example, an open access door or missing or punctured polythene blanks. Simple methods of locating any leakage are ; by listening for them ; by feeling for them espencially with a wet hand ; by applying soapy water over the seams or joints ; by (with the agreement of the client) using a smoke pellet.
NOTE : When smoke pellets are used, the smoke should be introduced downstre of the test rig and not on its intake side. 4.10.2
Reseal or correct where you have found the leakage source(s). Manufacturing faults should be reported to the factory immediately.
4.10.3
Repeat the test after allowing enough thme for the sealant to set. (Remember that sealants take longer to do this in cold weather. Read the sealant manufacturer's instructions.)
4.11 When satisfied with the results of the preliminary tests then ; 4.11.1 4.11.2 4.11.3
Offer the section to the client's representative for formal acceptance : On successful completion of the test obtain a signature - on the test sheet ; A permanent record of tests must be retained.
4.12 As tests are satisfactorily completed, remove all blanking off devices.
Relevant Conversion Factors Pressure To convert Multiply by Inches water gauge to milibars 2.49 Inshes water gauge to pascals (Pa) 249.1 1 Pa = 1 Newton per square metre = 10~2 millibars
Volume Flow To convert Litres per second to cubic metres per hour
Multiply by 3.60
Example of a completed test sheet Based on ductwork shown on page 10 and 11
page 7 of 40
Test No.
General Name of job Building Ref.
Part 1 - Physical details a b c d e f g
Senction of ductwork to be tested Drawing Number Pressure Classification Test static pressure Leakage factor Surface area of duct under test Maximum permitted leakage
(PRO (FROM DESIGNERS (FROM RE (FROM (OBTAINED B
Part 2 - Test particulars a b c d e f
Duct static pressure reading Type of flow measuring device Range of measurement of flow measuring device Reading of flow measuring device Interpreted air flow leakage rate Duration of test (normally 15 minutes)
Date of test
Carried out by
(READ OFF MAN (ALSO STATE MA (FROM RI
(DERIVED FROM CHARTSUPPLIE
Witnessed by
Width and depth or diameter
Periphery
Length
millimetres
millimetres
metres
squar
800 x 750
3100
17.550
5
600 x 650
2500
5.570
1
300 x 300
1200
1.200
1
305 dia.
958
7.000
6
250 dia.
785
4.500
3
TOTAL
page 8 of 40
8
Hints on Ductwork Leakage Testing Take special care with inaccessible joints
FLEX Keep length to a minimum and make sure that both end connections are the flexible dict itself has no leaks.
TEST APPARAT Site on firm level bas ensure gauges are to with correct fluid and zeroed prior to commencing test. Fit correct flow meas device.
In order to avoid incorrect readings of duct pressure the tube from the vertical manometer should be connected directly to the ductwork under test.
Inslined manometer to read leakage rate
SEQUENCE OFF TEST 1. Prepare test sheet. 2. Connect and adjust test apparatus to correct pressure. 3. Read off leakage rate. 4. Reseal if necessary (allow time to cure). 5. Maintain test for 15 mins. 6. Switch off and allow to zero. 7. Reapply test pressure and check reading. 8. Record details on test sheet and obtain signature.
page 9 of 40
WARNING Take care not to over pressurise system under test
The dimensions on this ductwork are used in an example on page 9
Blank off all open ends with polythene carefully taped in to position to avoid leaks. Remember to blank instrument tappings and test holes.
Vertical manometer to read duct pressure
Blank at convenient place with access for ease of removal 800 x 750
HOW TO FIND LEAKS 1. Look - particularly at blanks, access openings and difficult joints. 2. Listen - with test apparatus running, leaks should be audible. 3. Feel - running your hand (particularly if wet) over joints can help to locate leaks. 4. Soap and Water - Paint over joints and look for bubbles 5. Smoke Pellet - placed inside ductwork (obtain permission for use)
Part Two
page 10 of 40
This section is predominantly extracted from DW/142 - Specification for Sheet Metal Ductwork, and for ease of reference the numbering as in DW/142 has been retained. The leakage limits for EUROVENT classifications A,B and C, as set out in their ducument 2/2 (Air Leakage in Ductwork) have been adopted for the low pressure, medium pressure and high pressure Class C classifications. EUROVENT document 2/2 has no standard for a leakage class equivalent to our Class D and therefore the leakage limits for high pressure ductwork used in DW/141 (the predecessor to DW/142) have been retained.
6 AIR LEAKAGE STANDARS 6.1
6.2
Limits for each pressure class Permitted air leakage is related to four standards of airtightness, as set out in Table 2.
Compatibility with EUROVENT The leakage factors used in Table 2 for Class A, B and C are the same as those used for the classes similarly designated in the Eurovent Document 2/2 (Air leakage in Ductwork).
6.3
Leakage at various pressure : and other relationships Applying the limits specified in Table 2, Appendix A (Table 31) sets out the pernitted leakage at each of a series of pressures up to the maximum for each class. Included in that appendix is a graphical presentation of the pressure/ leakage relationship ; and also charts from which may be determined leakage as a percentage of airflow for classes A,B or C. Appendix A also gives details of the basis for the leakage limits specfied in Table 2.
6.4
Testing for air leakage All ductwork operating at pressure classified in this specification as high pressure' shall be tested to establish conformity with the relevant leakage limits set out in Table 2. Testing for leakage of ductwork within the low and medium ranges of pressure in this specification will not form part of the ductwork cintract unless this requirement is set out in the job specification - sec also Note(2) on page 1 of DW/142
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Table 2 Air Leakage Limits Air leakage 1
Leakage limits 2 litres per second per square Low-pressure - Class A metre of ducts surface area 0.027 xp .65 Medium-pressure - Class B 0.009 xp .65 High-pressure - Class C 0.003 xp .65 High-pressure - Class D 0.001 xp .65 where p is the differential pressure in pascals 0
0
0
0
APPENDIX A - AIR LEAKAGE FROM DUCTWORK
A.1
GENERAL CONSIDERATIONS
A.1.1
Leakage points in ductwork Air leakage in installed ductwork occurs almost entirely at the longitudinal seams and the cross joints, particularly at the corners, and at the intersection of the seams and cross joints.
A.1.2
Leakage related to duct area In practice, leakage can be taken as proportional to the surface area of the ductwork, whether rectangular or circular, even though there may be considerable variation in different sections of a complete system because of the changing sizes of the ducts and the number and variety of the fittings. The surface area is easily calculable as part of the design procedure.
A.1.3
Pressure/leakage relationship For a given pressure, the leakage through an orifice of a given area will vary according to its shape. With installed ductwork, the leakage orifices are of differing shapes, so a precise value cannot be given to the pressure/leakage relation shop. However, Swedish tests on a variety of constructions have shown that for ductwork operating within the range conered in this specification, leakage can be taken as proportional to pressure to the power of 0.65. (This value has been adopted by EUROVENT in preparing their Document 2/2 - Air Leakage in Ductwork - see Appendix L - and has also been adopted in this specification (see Table 2) and has been applied in Table 31.
page 12 of 40
A.2
LEAKAGE LIMITS - RELATIONSHIPS
A.2.1
Limits for each pressure class Applying the values given in Table 2 (page 13), the permitted leakage at each of a series of pressures up to the maximum for each class is set out in Table 31.
A.2.2
Graphical presentations The pressure/leakage relationships given in Table 31 are expressed graphically in Fig. 169.
A.2.3
Leakage as a percentage of airflow As air leakage is related to surface area of the ductwork, it cannot in advance of the detailed calculations be expressed as a percentage of total airflow, nor will a percentage loss be acceptable as a standard of performance. However, application of the leakage limits to a variety of ductwork systems indicates that under iparating conditions air losses will usually be within 6 per cent of total airflow for the low-pressure class and 3 per cent for the medium-pressure class. For the high-pressure class . Air loss is likely to be between 2 ans 0.5 per cent, according to which leakage limit is applied.
A.2.4
Special cases The percentages mentioned in A.2.3 apply to normal rations of duct area to normal ratios of duct area to airflow ; but where the ratio is high (e.g long runs of small ducts), it may be necessary for the designer to specify a higher standard of airtightness in order to keep the actual leakage within an acceptable limit.
A.2.5
a) b)
Designer's required calculations Designers will be concerned with the total loss of air through leakage which must be allowed for the ductwork, and will need to ; calculate the pressure class ; calculate the surface area and estimate the mean system pressure difference for the ductwork system (or part of system) ; Definition of mean pressure Pm = P1 + P2, where ; 2 Pm = mean or average pressure. P 1 = operating pressure at the beginning of the ductwork system or part of system. P 2 = operating pressure at the end of the ductwork system or part of system. IT IS RECOMMENDED THAT MAXIMUM TEST PRESSURES AND LEAKA SHOWN IN TABLE 32, PAGE 17, BE ADOPTED. page 13 of 40
c)
Calculate the total leakage using the appropriate rate from Table 31.
Alternatively, the designer may ; d) decide on the maximum total leakage that he can accept ; e)
A.2.6
calculate the wurface area and estimate the mean system pressure difference for the ductwork system (or part of system) and from these determine the required pressure class.
Leakage of complete system DW/142 deals only with the ductwork. The leakage characteristics of plant items and accessories are not within the control of the ductwork contracto and therefore any leakage limits and leakage testing called for under DW/142 shall be understood to apply only to the ductwork itself. Table 31 Air Leakage rates Static Maximum leakage of ductwork pressure Low-pressure Med-pressure High-pressure differential Class A Class B Class C Class D
1 Pa 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500
2
3
4
5
Litres per second per square metre of surface area
0.54 0.84 1.10 1.32 1.53
0.18 0.28 0.37 0.44 0.51 0.58 0.64 0.69 0.75 0.80
page 14 of 40
0.19 0.21 0.23 0.25 0.27 0.29 0.30 0.32 0.33 0.35 0.36 0.38 0.39 0.40 0.42
0.10 0.10 0.11 0.11 0.12 0.12 0.13 0.13 0.14 0.14 0.14 0.15 0.15 0.16 0.16
Fig. 169 Permitted leakage at various pressures
(a) LOW & MEDIUM PRESSURE CLASSES-LEAKAGE LIMITS
(b) HIGH PRESSURE CLASSES-LEAKAGE LIMITS
page 15 of 40
APPENDIX B - AIR LEAKAGE TESTING PROCEDURE
page 16 of 40
GENERAL
B.1
Section 6 (page 13) of this specification deals with the performance requirements of ductwork in respect or air leakage ; and Table 31 (Appendix A) tabulates the limits of leakage applicable to each class of ductwork. Appendix B is solely concerned with recommendations for the testing procedure.
Extent of ductwork to be tested
B.2 B.2.1
The procedure set out in this section is limited to the ductwork. Terminal connections, and items such as air handling devices, terminal boxes, soun attenuators, heat exchangers, builder's work construction, are e xcluded from the tests.
B.2.2
The proportion of the ductwork to be tested and the method of selection (where not included in the job specification) should be determined in collaboration between the designer and the ductwork contractor. Where th method is by random selection, the use of polythene sheet or similar insertion blamks between duct cross joints and duct-mounted components will assist in avoiding delays in installation when tests are being carried out.
B.2.3
To enable the blank to be cut out after the testing is completed, access may be required adjacent to each blank. This procedure used on either side of a duct-mounted component will enable the component to be includ in a sub sequent additional test if specified.
B.2.4
Alternatively, rigid removable blanking plates can be used, although this involves remaking joints.
Testing to be completed before insulation, etc.
B.3
Testing shall be satisfactorily completed before insulation or enclosure of the ductwork and before terminal units (if any) are fitted. B.4
Retesting procedure where necessary
B.4.1
The air leakage rate for any section shall not be in excess of the permitted rate for that section. If a first test produces leakage in excess of the permitted maximum, the section shall be resealed and retested until a leakage not greater than the permitted maximum for that section is achieved.
B.4.2
If at the time of witnessing the test it is apparent that excessive additional sealing of seams or joints has been done in order to meet the required leakage level, the section of ductwork under test shall not be counted as part of the tested ductwork, except where the whole of the ductwork is required to be tested.
page 17 of 40
Minimum area to be tested
B.5
The section of ductwork to be tested shall have an area large enough to enable the test aparatus to register a measurable leakage.
Test pressures and leakage rates
B.6
The maximum permissible leakage rates for the full range of pressures are give in Table 31. The recommended test pressures for the various classes of ductwor are set out in Table 32, and unless otherwise specified, the choice of test pressure shall be at the discretion of the test operator.
Table 31 Air Leakage rates Static Maximum leakage of ductwork pressure High-pressure Low-pressure Med-pressure differential Class A Class B Class C Class D 1 2 3 4 5 Pa Litres per second per square metre of surface area 200 0.84 400 1.32 0.44 800 0.69 1200 0.30 1500 0.35 0.12 2000 0.14 B.7
Test apparatus
B.7.1
The accuracy of the test apparatus shall be within ; ± 10 per cent of the indicated flow rate, or 0.4 litres per second, whichever is the greater ; and ± 5 per cent at the indicated static pressure in the duct under test.
B.7.2
the test apparatus shall be inspected by the user before use on site, and shall have a calibration certificate, chart or graph dated not earlier than one year before the test for which it is used.
B.7.3
A diagram of a suitable test apparatus is given in Fig. 171.
B.8 B.8.1
Procedure The section of ductwork to be tested for air leakage shall be sealed. Main ducts should be provided with flanged joints to enable blanking plate to be fitted, while small open ends may be sealed with polythene or inflatable bags, which should be left in position until final connections are made.
page 18 of 40
B.8.2
On low-pressure systems, final grille spigots made as a second fix operatio shall be excluded from the test. The joint shall, where practicable, be checked by external visual examination.
B.8.3
Sufficient time shall be allowed between erection and leakage testing for sealants to cure.
B.8.4
Special care must be exercised in making all joints which fall outside the scope of the testing procedure, i.e., joints between tested sdctions of ductwork and between ductwork and other units.
B.8.5
Due notice of testes shall be given, so that arrangements for witnessing the tests, if required, can be made.
Testing sequence
B.9
The recommended sequence fo testing is as follows. B.9.1
Complete Part 1 of the Test Sheet.
B.9.2
Connect test apparatus to section of ductwork to be tested.
B.9.3
Adjust test aparatus until the static pressure differential is obtained.
B.9.4
Check that the measured leakage is with in the permitted rate. (No assition shall be made to the permissible leakage rate for access doors, access panels or dampers where these are included in the ductwork.)
B.9.5
Maintain the test for fiften minutes and check that the leakage rate has not increased.
B.9.6
Reduce pressure in section to zero by switching off the fan ; then immediately re-apply test pressure to establish that the air leakage rate is not greater than the previous reading.
B.9.7
Record details on Part 2 of the Test Sheet and complete, including witnessing.
page 19 of 40
B.10 Air leakage test sheet A specimen of a suitable Test Sheet is given on page 9.
Fig. 171 Diagram of typical apparatus for air leakage tests Bleed valve(not necessary) Flow measuring device if variable speed
(may be located on
fan used)
the suction side of
Blanking plate
the fan)
Electrically driven fan Duct under tes
Dust test Inclined gauge
page 20 of 40
pressure gaug
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e,
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am
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IDED BY DESIGNERS) BY REF TO TABLE 32) F TO TABLE 31 OR 32) ALCULATION BELOW) MULTIPLYING AND f)
METER ON TEST RIG) NUFACTURER & TYPE) MANU. LITERATURE) (FROM RIG) WITH RIG USING"d")
rea
e metres .405 .925 .440 .706 .533
.009
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S e and pped up
uring
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E RATES
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r,
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e
ed
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k
s
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n
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